1. Field of the Invention
The present invention relates to a magnetic head assembly which projects light beams on a disk-shaped recording medium to position a magnetic head. More particularly, the present invention relates to a magnetic head assembly having a small dimension in a direction perpendicular to the recording surface of a recording medium.
2. Background Art
Most disk-shaped recording mediums prevalently used today are 3.5 inch diameter disks having a high track density in the range of about 2100 to 2500 TPI (tracks per inch) and a storage capacity in the range of 100 to 120 Mbyte.
The recording medium is provided with a position sensing track for optical tracking servocontrol for positioning a magnetic head relative to the recording medium. The position sensing track is used for closed-loop optical servocontrol for positioning the magnetic head relative to recording tracks.
FIG. 10 is a diagrammatic view of an optical system included in a conventional magnetic recording apparatus. Shown in FIG. 10 are a disk-shaped recording medium 50, a position sensing track 50a of a predetermined length formed continuously in concentric circles on one surface of the recording medium 50, a magnetic head 51 for writing information to the recording medium 50, or erasing or reading information recorded on the recording medium 50, a cartridge 50b for protecting the recording medium 50, and a rectangular window 50c formed in the cartridge 50 to enable the magnetic head 51 to gain access to the recording medium 50. The magnetic head 51 is bonded to a magnetic head support spring 51a, and the magnetic head support spring 51a supporting the magnetic head 51 is carried by a carriage unit, not shown. The magnetic head 51 slides on the surface of the recording medium 50 provided with the position sensing track 50a.
A light emitting-and-receiving unit 52 is provided with a laser diode 52a, i.e., a light source, and a photodiode 52b, i.e., a photodetection device.
A holographic unit 53 is provided with an optical element, not shown, for dividing light emitted by the laser diode 52a into three light beams, and an optical element, not shown, for guiding the reflected light reflected from the recording medium 50 to the photodiode 52b.
Shown also in FIG. 10 are a lens 54 for condensing light rays from the holographic unit 53 and guiding the reflected light to the holographic unit 53, and a mirror 56 for reflecting a light beam traveled through the lens 54 to the recording medium 50 and guiding the reflected light reflected by the recording medium 50 to the lens 54.
The above components 52 to 55 constitute an optical system. The optical system, the magnetic head 51 and the magnetic head support spring 51a are carried by a carriage mechanism, not shown, for simultaneous movement in directions parallel to the radius of the recording medium 50.
In operation, the recording medium 50 is rotated at a fixed rotating speed by a recording medium drive motor, not shown. The magnetic gap of the magnetic head 51 supported on the head support spring 51a slides on the recording medium 50.
Next, closed-loop optical servocontrol of the optical system will be described. Light emitted by the laser diode 52a is divided into three light beams by the holographic unit 53, the three light beams are condensed by the lens 54, the three condensed light beams fall on the mirror 55, and then the mirror 55 deflects the three light beams toward the recording medium 50.
The position of the light emitting-and-receiving unit 52 is adjusted so that the three light beams are arranged in a direction at a predetermined angle to the position sensing track 50a when the three light beams are projected on the position sensing track 50a.
The three light beams deflected toward the recording medium 50 by the mirror 55 are reflected toward the mirror 55 in reflected light beams of different intensities dependent on a condition in which the three light beams fall on the recording medium 50 or on the position sensing track 50a of the recording medium 50. The mirror 55 deflects the three reflected light beams toward the lens 54, the three reflected light beams travel through the lens 54 to the holographic unit 53, and then the holographic unit 53 guides the three reflected light beams to the photodiode 52b.
Upon the reception of the three reflected light beams, the photodiode 52b generates detection signals respectively representing the intensities of the three reflected light beams. A servocontroller, not shown, receives the detection signals from the photodiode 52b and gives a drive signal to a carriage drive unit, not shown, for driving the carriage mechanism, not shown, to drive the carriage mechanism according to the contents of the detection signals. The magnetic head (more precisely, the magnetic gap) carried by the carriage mechanism is positioned relative to a predetermined track by closed-loop optical servocontrol.
In the conventional magnetic head assembly thus constructed, the holographic unit 53, the lens 54 and the mirror 55 are individual components, those components are disposed below the magnetic head support spring 51a. Therefore, it is difficult to miniaturize the magnetic head assembly and to form the magnetic head assembly in a relatively small thickness, and hence the magnetic recording apparatus employing the same magnetic head assembly cannot be miniaturized and cannot be formed in a relatively small thickness.
Techniques for integrating the optical system with the holographic unit are disclosed in Japanese patent publication JP-A No. 4-219640. Those prior art techniques, however, concern an optical system for an optical pickup, go no further than facilitating the adjustment of the optical system and in miniaturizing the optical system by the integration of the optical system, and do not realize or suggest any means effective in forming a magnetic head assembly in a relatively small thickness.